Automatic and semiautomatic telephone system



Feb. 9, 1932. E. H. CLARK AUTOMATIC AND SEMIAUTOM-ATIC TELEPHONE SYSTEM Filed July 3, 1930 10 Sheets-Sheet l INVENTO/P B H. CLARK A TTORNEV Feb. 9, 1932. EH. CLARK AUTOMATIC AND SEMIAUTOMATIC TELEPHONE SYSTEM Filed July 3, 1930 10 Sheets-Sheet 2 N Ut INVENTOR E. H. CLARK A TTORNEY Feb.'9, 1932. CLARK 1,844,147

ww'ouxnc Aim SEMIAUTOMATIC TELEPHONE swrsmzm Filed July 3, 1930 10 Sheets-Sheet 3 Pic. .3

MARG/NAL INVENTOR E. H. CLARK I B) ATTORNEY Feb. 9, 1932. E. H. CLARK 1,844,147

'* AUTOMATIC AND SEMlAUTOMATIC TELEPHONE SYSTEM 'f'F'iled uly s. 1930 10 Sheets-Sheet 4 FIG. 4

lNl/ENTOR E H; CLARK B) A TTORNEY Feb. 9, 1932. CLARK 1,844,147

AUTOMAT I C AND S-EMIAUTOMAT I C TELEPHONE S [5 TEM Filed July 3, 1930 10 Sheets-Sheet 5 INVENTOR B E. H. CLARK A TTORNEV Feb. 9, 1932. E. H. CLARK AUTOMATIC AND SEMIAUTOMATIC TELEPHONE SYSTEM Filed July 3, 1950 10 Sheets-Sheet 6 WEOR Ra INVENTOR 6: H. C LA PK 8} ATTORNEY Feb. 9, 1932. E. H. CLARK AUTOMATIC AND SEMI'AUTOMATIC TELEPHONE SYSTEM Filed July 3, 1930 10 Sheets-Sheet 7 INVENTOR E. H. CLARK ATTORNEY Feb. 9, 1932. E. H. CLARK AUTOMATIC ANDSEMIAUTOMATIC TELEPHONE SYSTEM Filed July 3. 1930 mvsuroxe E .H. CLARK er ATTORNEY FIG. 84

Feb. 9, 1932. E. H. CLARK 1,344,147

AUTOMATIC AND SEMIAUTOMATIC TELEPHONE SYSTEM Filed July 3, 1930 10 Sheets-Sheet 9 E. H. CLARK ATTORNEY ew. UM

Feb. 9, 1932. E. H. CLARK' AUTOMATIC AND SEMIAUTOMATIC TELEPHONE SYSTEM Filed July 5, 1930 10 Sheets-Sheet 10 INVENTOR Lei/1.0mm 6? 6 M A TTORNEY l etented Feb. 9, 1932 umrsn stares Parent caries.

EDGAR I'I. CLARK, OF FOREST HILL$, NE'W' YORK, ASSIGNOR TO BELL TELEPHONE LABORATORIES, YORK INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW AUTOMATIC AND SEMLAUTOMATXC TELEPHONE SYSTEM Application filed July 3, 1930. Serial No. 465,484.

This invention relates to telephone exchange systems and more particularly to an impulse transmitting circuit which may be incorporated in any sender adapted to transmit to a terminating office a number of impulses determined by a group of operated registers. The object of the invention is to provide an improved arrangement of relays in a sender in which the registration of the wanted number is recorded, whereby the designations of such number may be transmitted more eiiiciently and economically b Y means of code impulses to the receiving circuit in the terminating ofiice.

Heretofore, the impulse transmitting system which forms part of some senders con sists, in the most general case, of a rotating device which, in combination with registers containing the record of the wanted number, generates a series of electrical impulses, the battery polarity and current density of each of which is controlled by the registers. There are other senders in which relays have replaced the rotating device, but it is believed that the present invention offers a distinct improvement over the latter as well as former class of senders, particularly as it combines a known method of precision impulsing in combination with less relays than formerly used and without the use of any mechanical apparatus, thereby resulting in a more efii cient and economical impulse transmitting system.

In accordance with the invention, therefore, one specific embodiment of which is disclosed herein by way of illustration, this is accomplished in the following improved manner through the use of novel circuit improvements which are covered by the patent applications of O. R. Miller Ser. No. 359,365 and 0f Cesareo Ser. No. 187,971 and to which reference is made for a complete description of theirrespective manner of operation.

There are five distinct types of impulses which are transmitted by the impulse system in the oroposed invention, namely, a blank impulse, a light positive impulse, a heavy positive impulse, a light negative impulse and a heavy negative impulse. A blank impulse is one in which no current is transmitted to the receiving circuit, but the pair of conductors, which are hereinafter designated as the impulsing conductors and termed tip lead and ring lead respectively, are open circuited. A light positive impulse is characterized as one having the grounded positive side of the battery on the ring conductor and the un grounded negative side of the battery on the tip conductor and having a current strength of definite value as determined by a high resistance in series with the tip conductor, the resistance of the call indicator receiving circuit of a type shown in Patent No, 1,438,743 to E. I LClark granted Dec. 12, 192:2 and the resistance of the trunk line connecting'the impulse transmitting circuit with the receiving circuit. Aheavy positive impulse is identical in character with the light positive impulse except that the current strength is greateras determined by the value of a resistance in series with the tip conductor and also the resistance of the receiving circuit and trunk line. A. light negative impulse is characterized as one having the grounded sideof the battery on the tip conductor, the ungrounded negative side of the battery on the ring conductor and having acurrent strength of definite value as determined by the value of a resistance in series with the ring conductor, the resistance of the receiving circuit and that of the trunk line. A heavy negative impulse is identical in character with a light negative impulse except that the current strength is greater as determined by the value of a resistance in parallel with the resistance used in the case of a light negative impulse. Y

The impulses to be transmitted are ar ranged in groups of four for each digit and providing for the transmission of a maximum of eight digits with a final heavy positive impulse for signaling purposes as described hereinafter. The impulses aretransinitted in a certain order with the odd impulses as either blank orlight positive and the even impulses as light or heavy negative. Five pairs of counting relays are i used, each pair being arranged in the manner disclosed in application Serial -No; 187,971

mentioned above. The front and back contacts respectively, of the relays of two of the five pairs are connected directly to the contacts of the separate registers, the operated condition of each of which determines r the character of the impulse to be transmitted as more particularly described hereinafter. The impulsing conductors over which the impulses are thus modified for transmission to the trunk line and to the receiving circuit in the terminating ofiice are connected to the switching contacts of the two pairs of counting relays through the medium of the contacts of the remaining three pairs of counting relays, which function to steer the said impulse modifying conductors from one group of wires connecting with the registers to the next group of wires in the order of succession in which the impulses are to be sent,

The i'mpulsing circuit itself which generates the impulses is disclosed in application Serial No.-359,865 mentioned above and consists of apolarized impulsing relay having two normally opposing windings, one of which is in series with a non-inductive resistance and condenser of suitable capacity. This impulsing relay is operated and re leased on the principle of opposing'magnetizing forces in both windings wherein the opposing force in the winding containing the condenser and resistance delays the operation of the relay until the condenser is fully charged to the potential of the battery. While the relay is thus in its non-operated condition a blank impulse is effective over the trunk loop unless the character of the impulse is, at this time, ehai-iged into a positive impulse by an electrical closure of the loop by the registers containing the recorded number as more particularly described hereinafter. The duration of this impulse is governed by the time taken for the condenser in the opposing windingto become fully charged. The length of time during which the impulse lasts is, therefore, a function of the capacity of the condenser and the ohmic resistance in series with it, which governs the rate at which the condenser thus becomes charged and hence the rate at which the opposing force is built against the magnetizing influence of the active or operating winding. When the condenser becomes fully charged and no further current can thus flow in the opposing winding the current in the active winding builds up to its full value, the relay operates, and the impulse is terminated. With the operation of the'impulsing relay two other relays in parallel are operated from its contacts, one of which relays controls the closure of the trunk loop with the proper battery polarity for a light negative impulse, while the other controls the successive operation and release of the two pairs of counting relays whose contacts are connected directly to the registers. These two pairs of counting relays, in turn, control the operation of the three other pairs of counting relays, so that, with each impulse, the character of the operated counting relay combination of the live pairs of relays is changed. With the operation of the above mentioned two relays in parallel, the impulsing conductors are reversed and the counting relays are operated. During the interval that the impulsing relay is in its operating position a negative impulse is transmitted, the current strength of which can be modified by operated registers as is described hereinafter.

Vith the operation of the impulsing relay the polarity of the condenser charging current is reversed, as is likewise the direction of current flow in the. active winding. The iinpulsing relay is thus made ready to release since, the relay being polarized, the current in the active winding will flow in the wrong direction. In this case however the discharge condenser current in the opposing winding delays the immediate rise of the current in the active winding and conse- .rjf

quently delays the release of the relay until the magnetizing force of the active winding is greater than the force in the opposing winding. In this case also the length of the negative impulse is measured by the time taken for the impulsing relay to release which, as mentioned above in connection with the positive impulse, is a function of the electrical time constant of the condenser and resistance combination in series with the oping relays are operated once more and a positive impulse is thereafter transmitted if the register to which the other trunk conductor is now connected closes the proper polarity battery thereon; otherwise it will be a blank impulse. impulsing relay is repeated in this manner, the impulses being sent out in alternate succession of blank or positive and negative int pulses, while the three pairs of steering counting relays progressively transfer the impulse modifying conductors from one group of contacts connected with the registers to the next in the numerical order in which the impulses are to be sent out. When the last group of impulses is transmitted at special heavy positive impulse is transmitted for the purpose of closing through. the circuits of automatic selector switche in the ctstant offices through which the trunk line may have been routed in order to reach the terminating office where the impulses are received, if the connection has been so routed.

It is seen that the impulses generated by the impulsing circuit thus describ d consist of either blank or light negative impulses.

The operation and release of the y These impulses are modified either to light positive or heavy negative by the operated or non-operated condition of the registers con-- taining the recorded number when, during the transmission 01" each impulse, the impulsing modifyin conductors are switched progressively from one group oi registers to the next. The modification of the blank and light negative impulses generated by the impulsing circuit consists either in transforming a. blank impulse into a light positive impulse by the register connecting battery on the tip conductor during the transmission ot a positive impulse or transforming a light negative impulse into a heavy negative impulse by the register placing battery through a low resistance in parallel with the battery through the high resistance to the ring conductor during the transmission or" a negative impulse. The modified im )ulses serve to operate marginal and polarized relays i the receiving equipment which control the operation of numerical registers and associated lamps to display the number represented by the positive and heavy negative impulse codes thus transmitted. lhe light negative impulses control the switching relays -1 the receiving circuit for transferring the record of the impulses received to the appropriate group of numerical registers.

When the exchange code and number of the wanted subscriber is recorded on the registers of a sender. and trunk line to the desired terminating office has been selected by the automatic switches, an assignment lamp, individual to the selected trunk, is lighted at the operators position where the trunk terminates. The sender is, at this time, connected to the trunk in question and is ready to respond to a signal from the operator at the distant office, which signal is given when an assignment key is depressed in response to the ighting of the assignment lamp. The depression of the key causes the trunk conductors to be connected to the impulse receiving circuit at the operators position and, at the same time. causes the release of a relay in the sender. The release or" this relay is the signal awaited by the sender for connecting the impulsing circuit to the line and extending the impulse mocitying conductors to the registers by way of the counting relays. The impulses corresponding in code form to the number recorded in the registers are then transmitted in the manner already described; the sender extending the impulse modifying conductors through the steering counting relays, in proper coml-iination. to the conductors of the registers containing the recorded numher and which are to transmit heir impulses in the order in wh ch the said impulse modifying conductors are connected to theseparate relays oi the registers. lVhen all the impulses have been sent he relay which first connected the trunk conductors to the impulse circuit is released and other circuits are then closed to release the sender and restore it to normal. 7 V

A clearer conception of the scope and pur pose of the invention will be obtained from 1? a consideration of the following description taken in connection with the attached drawings in which Figures 1 to '9, wiien arranged in the order illust'ated in the diagram of Figure 11, discloses as much of the telephone Figure 2 shows a portion of the detailed circuits of one of the trunks outgoing from the line switch of Figure 1 and also a dia gram of a'coordinate group selector switch in which said trunk terminates.

Figures 4, 5, 8, 8A and 9, taken together, show one of a number of register sender controlling mechanisms incorporating the invention herein described and which is associable with the trunks by means of the sender selector switch illustrated in Figure 1.

Figure 4 illustrates the dial impulsing relays and other control relays of the sender.

Figure 8 shows the controlling relays for sending code impulses representing the re corded designations.

Figure SA shows the counting relays which are associated with the control relays of Figure 8 and the relay registers of Figures 5 and 9.

Figures 5 and 9, taken together, show relay registers on which designations are recorded under the control of the calling subscribers line.

Figure 3 illustrates the incoming end of an interoihce trunk circuit. This trunk terinmates in a plug-ended cord circuit at a manual operators position in the called office. This figure also shows a called subscribers line terminating at a manual otlice.

Figures 6 and 7 show a register circuit serving the purpose of a call indicator.

Figure 10 shows a chart indicating the character of the impulses transmitted tor the digits Zero to nine, inclusive.

The line switch 100, the group selector switch 200 and the sender selector switch 110 are of the coordinate type such as shown and same time the trunk 103 is associated with an idle register sender by means of the sender selector switch 110. Following this, the subscriber dials a number of digits which are recor led on the several registers of the associated sender. Thereafter, in any suitable manner, the register sender determines the selective operation of the district selector switch 200 from the number of the recorded digits which indicate the route, and an idle trunk is selec ed leading to the distant manual office at which it appears. Inasmuch as the irese'ntinvention is not concerned with the detailed description of the selector switches, nor with the manner in which the register sender exercises its control over the switches, several elements have been illustrated in schematic fashion. For amore detailed explanation of the way in which the operating circuits of the various switches function and the manner in which the register sender controls the selection of trunks, reference is made to Patent 1,517,331 granted December 2, 1924 to S. B. Williams.

After a trunk has been selected by switch 200 in the mechanical office leading to the distant manual ollice illustrated in Figures 3, 6 and 7, it is necessary to transfer the record established in the register sender over the trunk to the distant office to bring about the operation of the call indicator in order that the operator may be adv'sed of the called line number. This is accomplished by means of the equipment shown in Figure 5, 8, 8A and 9 particularly illustrating the present invention, wherein the relay devices 807 and 808 control operations which result in the creation of impulses which form codes according to the record established on the registers and transmits these impulses over the line to the distant manual oflice. The record is established on the distant manual ofiice in the call indicator registers and causes the illumination of the proper lamps before the operator. In case the distant called oiiice is one involving machine switching apparatus for build ing a connection, code impulses will be transferred to a register sender thereat which, in turn, will control the operation of switches in the distant called office.

A detailed description will now be given of the establishment of a connection between a calling line in a mechanical oliice, such as line 101, and a called subscribers line, such as line 319 in a distant manual office, involving the transfer of the called line record from the first office to the second otlice over a direct trunk. Assuming that the entire designation of the called number is 2531345 wherein the first three digits indicate the designation of the called otlice and the remaining four digits the numerical designation of the called line in that oilice, all these digits are recorded on seven of the eight registers shown in Figures 5 and 9, namely, registers 900, 909,

"' 912, 026, 512, 513-and 521 in the order named.

If the called subscriber is on a party line, an additional digit will be dialed indicating the station and this digit will be recorded on register 518.

When the calling subscriber initiates a call, his line 101 is extended automatically through the line switch 100 to the first idle one of a number of outgoing trunks 102, 103, etc. If the trunk 103 is the first one to be idle, it is selected and the called line is extended thereover to the district selector switch 200. At the same time that the calling line is extended to the district selector, the sender selector switch 110 is operated automatically and the trunk 103 is connected to the idle register sender shown partially in the drawings of Figures 4, 8, 8A, 5 and 9'.

During the operation of the sender selector switch 100, a circuit may be closed in any suitable manner for relay 204. Relay 204 operates and applies ground potential to the holding or sleeve conductor 111. As soon as the sender selector switch 110 is operated, it may complete a circuit in any suitable manner for relay 203. Relay 203 operates and,

at its bottom outer contacts, closes a substitute circuit for the slow releasing relay 204. Relay 203 also extends the tip and ring conductors 104 and 105 of the trunk through the sender selector 110 to the selected sender by way of conductors 221 and 220, respectively. An impulse circuit is now traceable from battery through resistance 434, right winding of relay 400 in the sender, normal inner con tacts of relay 401, conductor 418, left outer contacts of relay 411, through selector 110, conductor 220, bottom inner make contacts of relay 203, conductor 105, through the line switch 100, over the loop of the calling line and returning through the line switch 100 to the conductor 104, top inner make contacts of relay 203, conductor 221 through the selector 110, left inner contacts of relay 411, outer contacts of relay 401, left winding of coil 402 to ground. Relay 400 closes a circuit for slow release relay 404 which, in turn, closes on its left contacts a circuit for relay 410. Relay 410 operates and, on its left inner contacts, applies holding ground to conductor 420 which provides holding circuits for the sender selector switch 110 and for relay 208 in the trunk circuit. Relay 400 also closes a parallel circuit through the left winding of relay 403 which relay operates and closes a circuit for relay 425 extending from battery, resistance 405, left contacts of relay 406, right contacts of relay 403, conductor 407, left back contacts of relay 408 through both windings of relay 425 in series to ground. Relay 425 operates and locks in a circuit extending from battery through resistance 405, conductor 409, left contacts of relay 412, conductor 413, right inner contacts of relay 425, right winding of relay 425 to ground. Relay 425 also closes a circuit for relay 421 extending from battery and left winding of relay 403, left inner contacts ofrelay 403, left outer back contacts of relay 422, right outer back contacts of relays 422, 423 and 424, left outer front contacts of relay 425 through both windings of relay 421 in series to ground. -This circuit, however, is ineffective at this time due to the direct connection from the left front contact of relay 403 to ground through the front contacts of relay 400, thus keeping relay 421 short-circuited at this time. The apparatus is now in condition for receiving the first series of impulses.

The operation of the counting relays shown in 4 in response to dial pulses forms the subject matter of Patent No. 1,563,738, granted on December 21 1925 to O. C. From. Remembering that the number assumed to be dialed is 253-1346 the calling subscriber now manipulates the dial or other impulse transmitter to send a series of two impulses or interruptions of the impulse circuit. In response to the first interruption of the circuit, relay 400 releases and permits the above traced circuit for relay 421 to become effective, whereupon relay 421 operates and locks in a circuit from ground through its right Winding and right inner contacts, conductor 413, left contact of relay 412, conductor 409, resistance 405 to battery. Relay 421 also closes a circuit from battery through resistance 405 on conductor 413, right inner confacts of relay 425 through the left winding of relay 425, left inner contacts of relay 421 to ground through the right winding of relay 403, the current in which circuit opposes that in the locking circuit for relay 425 and releases relay 425 differentially. The looking circuit for relay 421 is in shunt of its energizing circuit through the left winding of relay 403 and tends to release relay 403. The circuit through the right winding of relay 403 which releases relay 425 is diderential to the circuit of the left winding of re lay 403, so that with relay 400 released, relay 403 releases quickly upon the operation of relay 421.

At the time relay 400 falls back in response to the first impulse, a circuit is closed from ground on the back cont-acts of relay 400, right contacts of relay 404, winding of relay 406 to ground. Relay 406 operates and opens the initial energizing circuit for relay 425. Relay 406 als closes an obvious circuit for relay 408. Belay 408 operates and locks in a circuit from battery through its winding and left inner contacts right middle back contacts of relay 412, left outer contacts of relay 410 to ground. Relay 408 closes circuits the purpose of which will be made clear hereinafter.

At the end of the first impulse interruption, relay 400 again attracts its armature, relay 403 is operated and a circuit is C011lpleted for relay 422 byway of battery through the left Winding and left inner contacts of relay 403, right outer front contacts of relay 421, right outer back contacts of relays 423 and 424, left outer back contacts of relay 425 through both windings of relay in series to ground. Belay 422 does not operate at this time as it is shunted by the ground on the front contacts of relay 400. llelay 406, being slow to release, does not rctr ct its arniatures during the time that a train of impulses is being transmitted.

At the next interruption of the circuit, relay 400 falls back permitting relay 422 to operate in series withthe leftwinding of relay 403. Relay 422 operates and locks to battery through resistance 405 over conductor 413-and closes a differential releasing circuit for relay 421 extending from ground through the right winding of relay 403, left inner contacts of relay422, left winding of relay 421,

right inner contacts of relay 421 to conductor 413. Relays 421 and 403 release.

At the closure of the line after the second impulse, the first train of impulses'is terminated and relay 400 remains energized long enough to permit relay 406 tode-energize and retract its armatures. Since relay 408 was operated and locked, a circuit is closed from ground on the right normal contacts of relay 406, right inner contacts of relay 408, right inner contacts of relay 412, conductor 416, right back contacts of relay 901, winding of relay 902 to battery. Relay 902 attracts its armatures and locks in a circuit including its top inner contacts, conductor 903, winding of relay 412 and thence over the above traced circuit to ground at the right normal contact of relay 406. Relay 412, being shunted by the operating ground for relay 902, does not energize at this time. Belay 902 extends conductors 419, 429, 439 and 449 to the relays of the first code digit register 900. Since relay 422 is the only counting relay'operated as a result of a train of two dialed impulses, a'circuit may be tracedfrom ground atthe left middle contacts of relay 410, right outer con-' tacts of relay 412, conductor 415, right outer back contacts of relay 425, left outer back contacts of relays 424 and 421, conductor 429,"

No. 2 contacts of relay902, Winding o-frelay- 904, winding of relay 905 to'battery. Re: lays 904 and 905 operate and lock in a circuit from battery, windings of the two relays, right inner contacts of relay 904, conductor 906, conductor 907, conductor 426, right outer contacts of relay 410 to ground. Relay 905 closes a circuit for relay 901 from ground on conductor 906 operating this re lay and locking it to ground on conductor 906. As its right back contacts, relay 901 opens the shunt around the Winding of relay 412, permitting that relay to energize in series with the locking circuit of relay 902.

Relay 412, at its left contacts, opens the looking circuit of the counting relays and, at its right outer contact, the locking circuit of relay 408. The counting relays are restored to normal. Relay 408 releases and opens the circuit of relays 412 and 902 disconnecting the register 900 from the counting relays. As soon as relay 412 falls back, the original circuit for relay 425 is closed again and that relay energizes and prepares a circuit for relay 421 as before.

The subscriber next dials the second digit of the called number, that is 5. In response to the first-interruption of the dialing circuit relay 406 is energized, in turn energizing relay 408. Relay 421 is operated and relay 425 released. In response to the next interruptionof thecircuit, relay 422 operates and relay 421 releases. In response to the third interruption of the circuit, relay 423 is energized in a circuit from battery through the left winding of relay 403, left inner contacts of relay 403,, right outer back contacts of relay 421, right outer front contacts of relay 422 through both windings of relay 423 in series to ground. Relay 423 attracts its armatures and releases relays 422 and 403 in a manner similar to that for the other counting relays previously described. In response to the fourth circuit interruption, the circuit prepared for relay 424, extending from battery through the left winding and left inner contacts of relay 403, right outer back contacts of relays 421 and 422, right outer front contacts of relay 423 through both windings of relay 424 in series to ground, becomes effective and relay 424 attracts its armatures, releasing relays 423 and 403 and locking to conductor 413. The fifth interruption of the dialing circuit causes the; operation of relay 425 in a circuit from battery through the left winding and left inner contacts of relay 403, right outer back contacts of relays 421, 422 and 423, right outer front contacts of relay 424, the two windings of relay 425 in series to ground. Relay 425 looks to conductor 413 through its right winding and release relays 424 and 403. Relay 425 also completes a circuit from battery through the winding of relay 427, rightcontacts of relay 428, right outer contacts of relay 408, right outer front contacts of relay 425, conductor 415, right outer contacts of relay 412, left middle con tacts of relay 410 to ground. Relay 427 operates and locks in a circuit through the Winding of relay 428right contacts of relay 427 conductor 417 right outer contacts of relay 412 to ground on the left middle contacts of relay 410. Relay 428 cannot operate ber ing shunted by the energlzmg circuit of relay 427. ,WVhen, at the close of this series of impulses, relay 400 remains energized for a considerable period of time, relay 406 releases and completes a circuit from ground. on the right normal contacts of relay 406,

rightinner contacts of relay 408, right inner contacts of relay 412, conductor 416, right front contact-sci? relay 901, right back contacts of relay 927, winding of relay 908 to battery. Relay 908 operates and locks in a circuit including its top inner contacts, con-- ductor 903, winding of relay 412, right inner contacts of relay 408, to ground on the right normal contacts of relay 406. Relay 908 extends conductors 419, 429, 439, 449 to register 909. Since relays 425 and 427 are operated, a circuit is closed from ground at the left middle contacts of relay 410, right outer contacts of relay 412, conductor 415, right outer front contacts of relay 425, right outer contacts of relay 408, left inner contacts of relay 427, left inner contacts of relay 428, conduo tor 449, No. 4 contacts of relay 908, winding of relay 910 to battery. Relay 910 operates and locks by way of its left inner contacts, conductor 911 to grounded conductor 907. Relay 910 also connects ground from conductor 911, left outer contacts of relay 910, winding of relay 927 to ba tery. Relay 927 operates and locks to conductor 911. The operation-0f relay 927 opens the energizing circuit for relay 908 which was in shunt of the winding of relay 412 and relay 412 operates. Relay 412 opens the locking circuit for the. counting relays and'that of relay 408. Relay 408 in releasing, opens the circuits of relays 412 and 908, whereupon these relays also release and the circuits of Fig. 4 are ready to receive the next series of impulses.

Relay 400, being ener ized at the time, as

soon as relay 408 closes its left outer contacts, the previously traced circuit for relay 425 is closed and that relay prepares a circuit for relay 421 as before.

The calling subscriber now manipulates his dial to send a series of three impulses, which represents the last digit of the oiiice code. Relays 406 and 408 are operated at the first interruption of the dialing circuit and,

at the end of the third interruption of the circuit, relay 423 is operated and the other counting relays de-energized. Relay 400, remaining energized thereafter for a considerable period, permits rela '406to release. A circuit is then closed from ground on the right normal contacts, of relay 408, right inner contacts of relay 408, right inner contacts of relay 412, conductor 416, right front contacts of relays 901 and 927, right back con tacts of relay 913, winding of relay 923 to battery. Relay 923 operates and locks in a circuit through its top inner contacts, conductor 903, winding of relay 412, right inner contacts of relay 408 to ground on the right normal contacts of relay 406. Relay 923 extends conductors 419, 429, 439, 449 to therelays of register 91.2. Since relay alone is energized, a circuit is closed from ground at the left middle contacts of relay410, right outer contacts of relay 412, conductor 415,

right outer back contacts of relay 425, left outer back contacts of relay 424., left outer contacts of relay 4L3, conductor 419, No. 1 contacts of relay 923, winding of relay 918 to battery. A circuit is also closed from ground on conductor 415, right outer back contacts of relay 425, left outer back contacts of rclay 424, left outer back contacts of relay 421, conductor 429, No. contacts of relay 923, winding of relay 914 to battery. Relays 913 and 914 operate and lock by way of conductor 916 to grounded conductor 907. The operation of these relays also extends ground from conductor 916 to relay 913. which relay operates and locks to conductor 916. The operation of relay 913 opens the energizing circuit of relay 923, permitting relay 412 to energize and bring about the release of the counting relays as before.

The calling subscriber next operates his dial to send a single impulse which represents the first digit of the called subscribers number. In response to this impulse, relay 421 is operated and relay 425 released. At the completion of the impulse, relay 406 releases and a circuit is completed from ground though the right normal contacts of relay 406, right inner contacts of relay 408, right inner contacts of relay 412, conductor 416, right front contacts of relays 901, 927 and 913, right back contacts of relay 919, winding of relay 917 to battery. Relay 917 operates and locks by way of its top inner'contacts, conductor 903, winding of relay 412 and thence over the previously traced circuit to ground. Due to the energization of relay 421, a circuit is closed from ground on conductor 415, right outer back contacts of relay 425, left outer back contacts of relay 424, left outer front contact of relay 421, conductor 419, No. 1 contacts of relay 917, winding of relay 920 to battery. Relay 920 operates and locks by way of conductor 921 to groundeo conductor 907. In addition, relay 920 closes an obvious circuit for relay 919 from ground on conductor 921. Relay 919 operates and locks to conduc tor 921. Relay 919, on operating opens the circuit in shunt of relay 412 and this relay energizes and brings about the restoration of the counting relays and the disconnection of register 926 from the energizing conductors.

The subscriber next dials the series of impulses representing the digit 3 and, by the dialing circuit operations identical with those previously described for the digit 3 of the otfice code, relay 505 is operated,'whereupon relays S and 509 of register 512 are operated and locked. The operation of these relays closes obvious circuits for relay 500 which, on operating andlocking to ground through conductors 510 and 426, transfers the register cut-in circuit to relay 504 of register 513.

The subscriber next dials the series of impulses representing the digit 4. Through the means of circuits previously described, relay a circuit is closed from ground on the right normal contacts of relay 406, right inner contacts of relay 408, right inner contacts of relay 412, conductor 416, right front contacts of relays 901, 927, 913, 919 and 500, right back contacts of relay 501 winding of relay 504 to battery. Relay 5 4 operates and lock to grounded conductor 903. A circuit is closed from ground on the left middle contacts of relay 410, right outercontacts of re-. lay 412, right outer back contacts of relay 425, left outer front contacts of relay 424, conductor 439, No. 3 contacts of relay 504, Winding of relay 514 to battery. Relay 51 looks to ground on conductor 516 and closes an obvious circuit for relay 501 which also operates and locks to ground on conductor 516 and thereafter opens the energizing circuit of relay 504. This operation removes the shunt around relay 412 which operates and restores the dialing circuit in preparation for the next. digit. I The subscriber next dials the series of impulses representing the digit 6 which is the last digit of the called number. The dialing of five of the six impulses proceeds in the same manner as previously described for the impulses of the digit 5 of the OfilCG code. It will be recalled that, at the termination of the fifth impulse, relay 425 was operated and likewise relay 427. Relay 428, however, re-

mained shunted due to the presence of the operating ground for relay 427011 the left side/of the Winding of-relay 425. lVhen, however, the sixth impulse is receiv d and relay 421 is operated, relay 425 is released bythe shunting ground through the right winding of relay 403 and the left inner front contacts of relay 421 so that the short circuit around relay 428 is removed, causing this relay to operate and lock in series with. relay 427 to ground on the left middle cont cts' of relay 410. lVhcn the Sli t-ll impulse is thus received and terminated, a circuit is closed from ground on the right normal contacts of relay 406, left inner front contacts of relay 408, right inner contacts of relay 412, conductor 416, right front c ntacts of relays 901, 927, 913, 919, 500 and 501, right back contacts of relay 502, winding of relay 503 to battery. Relay- 503 operates and locks through its top inner contacts to ground on conductor 903. Circuits are also closed from ground on the left middle contacts of relay 410, right outer contacts of relay 412, right outer back contacts of relay 425, left outer contacts of relays 427 and 428 to conductor 449, While another branch of this circuit is extended from the rightouter back contacts of relay 425 to the left outer back contacts of relay 424, left outer front contacts of relay battery. Likewise, conductor 419 421 to conductor 419. Conductor 449, over path previously traced, is extended to the the No. 4 contacts of relay 503 and from thence through the winding of relay 515 to extended over No. 1 contacts of relay 503 and from thence through the winding of relay 517 to battery. Relays 515 and 517 operate, lock to grounded conductor 511 and close obvious circuits for relay 502 which also operates and loci-Is to grounded conductor 511. l he operation of relay 502 opens the energizing circuit of relay 503 and removes the shunt around relay 412 causing it to opcrate and restore the dialing circuit for the reception of further digits.

he subscriber has now dialed the entire number. Should it be, however, that the called subscriber is on a party line and a corresponding letter designation is necessary, the impulse designation of the party letter will be recorded on register 513 in the same manner as described for the dialing of any of the previous digits.

After the subscriber has set up the oifice code record on registers 900, 909 and 912 the district selector switch 200is-operated under the control of these registers and cooperating circuits in the sender for the purpose of selecting an idle trunk 207 extending to the distant called oiiice. These circuits are not shown as they form no part of the present invention and can be arranged in any suitable manner with the cooperating circuit elements of the sender tor the performance of this function. During the operation of switch 200, relay 206 is operated and locked through its top inner contacts, conductor 210, top outer contacts 01" relay 203 to the grounded conductor 111. Upon the operation of relay 206, relay 205 is operated by the switch 200 in a suitable manner and looks through its left armature to conductor 210.

After the connection has been extended to the distant office, the apparatus is placed in condition to transmit code impulses over the trunk in accordance with the settings of the numerical registers in Figs. 5 and 9, that is, registers 926, 512, 513, 521 and, if a party letter has been dialed, register 518 also. Then, after a suitable time delay has been allowed to permit the subscriber to dial a party letter, and the circuits in the sender are ready to transmit the impulsesdesignating the wanted number, a circuit is completed, in any suitable manner, for relay 440. A circuit is also closed in any suitable manner,

for relay 802 it, from the translation of the oflice code registration contained in registers 900. 909 and 912, circuits are closed in the sender which indicate that the call is to be completed over a direct route to a manual otlice having call indicator apparatus therein. The manner in which the above mentioned operations take place is shown and described in detail in Patent No. 1,517,331, granted December 2, 1924 to S. B. Villiams. Relay 440 closes a circuit from battery through the winding of relay 441,, contacts 01- relay 440 to ground on the right inner contacts of relay 410. Relay 441 operates in this circuit, locks through its left contacts to the operating ground and connects relay 446 through its right contacts to the tip and ring conductors of the trunlr line resulting in a circuit as follows: Battery through the bottom inner back inner contacts of relay 300, conductor 301, right winding of relay 302, winding of relay 303, inner normal contacts of relay 304, outer back contacts of relay 305, thence over the tip side of the trunk 207 through switch 200, top outer front contacts of relay 206-, right innercontacts of relay 205, conductor 211, through the selector switch 110, conductor 431, right inn-er contacts of relay 441, right inner back contacts of rela 443, windi. g of relay 446, right outer bac 110, conductor 212, right outer contacts of relay 205, bottom outer front contacts of 206 through the switch 200, thence over the ring side of the trunk line 207, inner back contacts of relay 305, outer normal contacts 1y 304, left winding of relay 302 to Relays 302 and 303 operate and relay closes a circuit for relay 306. Relay 306 operates and, at its left outer contacts, closes a circuit around relay 303, releasing thi s relay and preventing it from reoperating in series with the right winding of relay 302. Relay 306 also closes a circuit from battery through the assignment lamp 307, lower winding of relay 308, right outer back contacts of relay 309, top inner contacts of relay 308, right inner contacts of relay 306 to ground. Lamp 307 lights to advise the operator tint a callis awaiting attention on the incoming trunk 207. Due to the character of relay 308, however, it is not energized suiticiently to attract its armature.

The code impulses are sent to the receiving oiiice over a full metallic circuit comprising both tip and ringconductors or" the line in series. These impulses may be of either positive or negative polarity dependent upon the side of the line circuit to which the positive pole of the battery is connected. They may also be weak or strong, dependent upon whether the battery is fed to the line through a high or low resistance. The impulses are received by the relays 601, 602 and 603. Relay 601 is polarized in such a manner as to respond only to the current produced when the positive pole of the battery is connected to the tip side of the line. Relay 602 is polarized in such a manner as to respond to current 0% the opposite polarity. Both relays 601 and 602 respond either to strong or weak impulses provided the polarity is in 302 and 303 and closes an obvious circuit for relay 445. Relay operates and closesa circuit from groundon the right lnner contacts of relay 410 to the Winding of relay 444 which operates and locks to the same ground. 7

Returning to the called ofiice, the operator, observing the illumination of lamp 307, presses the individual assignment key 310 to associate the call indicator with trunk 20?. Key 310 closes a circuit from battery through the winding of relay 605, conductor 628, bot-- tom contacts of relay 308, rightwindingof relay 309, top contacts of key310, conductor 324, contacts of relay 624 to ground at theright back contacts of relay 620. Relay 309 operates and locks in a circuit from battery through winding of relay 605, conductor 628 bottom contacts of relay 308, windings of relay 309 to ground on its left contacts. Re lay 309 opens the original circuit of lamp 307 and connects this lamp in series with interrupter 311; The lamp flashes during the period that impulses are received, as described hereinafter, and until the operator inserts the trunk cord plug into the jack of the called line. Relay 309 also closes a circuit from battery through the winding of relay 305 and in parallel with battery through the left winding of relay 312, right inner contacts of relay 309, conductor 629 winding-of relay 6'24 to ground at the left back, contacts of relay 620. Relay 305 operates. and extends the tip and. ring conductors of :the incoming trunk to conductors 600 and 604 respectively. When relay 305 operates it opens thecircuit including relays 302 and 446. Relay 302 releases and opens the circuit of relay 306 which also deenergizes. The release ofrelay 446 permits the release of 445,,

which relay now completes a circuit from battery through the winding of relay 443, outer contacts of relay 444, back contacts of relay 445 conductor 430 to ground'onthe right inner contacts of relay 410. Relay-443 disconnects relay 446' from the trunk conductors, connects them to the impulsing circuit shown in Fig. 8 by way of conductors 447 and 448 and closes a circuit for relay 800 from battery through the winding of relay 800, conductor 801, left inner contacts of relay 443, conductor 433, No. 4 contacts of relay 803, top contacts of relay 802 bottom middle back contacts of relay 804 to ground. From} this moment on, the impulse circuit begins to transmit impulses in codes, controlled by the operated relaysin the various registers'of' Figs. 5 and9. r v

Relay 800, when it operates, closes a -num ber of circuits as follows: ground'on the bottom outer back contacts of relay 804, right Nos. 1, 2 and 3 contacts of relay 800, conductor 805, winding of relay 806, resistance 809 to battery. Also another circuit from the same aforetraced ground Nos. 1 and 2 contacts.

of relay 800, conductor 810, winding of relay 811, resistance 812 to'battery. Relay 806 operates in the former circuit, lockingto ground throughits rightinner front contacts, conductor 848 to the left outer contacts of relay 410,

andrelay 811 operates over the latter circuit and looks through its left inn-er front contacts, conductor,- 848 to ground. During the period thatrelay 806 is still normal, but in,-

preparation for operating by the closure of the aforetraced energizing circuit, relay 816 remains short circuited by the connect-ion of operating ground on conductor 805 to the right side of its winding and also the same ground on its other side byway of the left inner back contacts of relay 816-conductor 87 3 to the right normally made contacts of relay 806. When, however, relay'806 has operated and opened these normally made contacts, relay 816 operates over a circuit from battery, through resistance 825, winding of relay 816, right inner front contacts of relay 806 to ground on conductor 848. Likewise, relay 817 will remain short circuiteduntil relay 811 opens its left inner nor-' mally made contacts and, when this occurs, relay 817 will operate in a circuit from loat-v tery through resistance 826, winding of re-- lay 817, left inner front contacts of relay 811 to ground on conductor-848. The operation of relay 811 closes a circuit from ground 818, resistancev 841 to battery. Relay 818 operates'and looks over its left innermost front contacts to ground on conductor 848.

Relay 819, which is. paired with relay 818,

remains short circuited due to the presence of the locking ground for relay 818 on the right side of its winding and ground from the right inner front contacts of relay 811 on the left side of its winding by way of conductor 87 2 and the No. 1 back contacts of relay 819.

When relay 816 operates, a circuit is closed from ground on the left inner front contactso'f relay 800, conductor 827, right outer contacts of relay 816, conductor 840, winding of relay 804 to battery. Relay 804 operates and locks over its top outer contacts to ground at relay 802' and opens the circuit of relay 800 which releases." Relay 804 closes ground through. its top middle-front contacts, top back contacts of relay 807, resistance 841 to battery and also a. parallelcircuit extending from resistance 841, through resistancc829,bottom winding of impulse relay808, resistance 832 to battery. At the same. time that this circuit .is established, yet

another circuit is closed in parallel with the foregoing circuit through resistance 828, resistance 830,- condenser' 831, upper winding; of impulse relay 808, resistance 832' to battery.

Relay 808 tends to operate because of the energizing circuit through its lower winding. However, the charging? circuit through the condenser 831 and upper winding overcomes the energizing circuit during the time requiredto charge the condenser, so that d1rr- I0 ingthe: charging period, relay 808 remains normal. In the meanwhile a circuit is established from ground on the bottom middle front contacts of relay 804 to the back con tacts' of relay 807 and from these contacts two parallel circuits are established, one by wayof conductor 835, normally made corn tacts of the No. 1 contact set of relay 824,:

winding of relay 824, resistance 892 to bat-V tery, and the other by way of conductor 833, normally made contacts of the No. 4- contact set of relay 815, winding of relay 815, re sistance 834 to battery. Both of these relays energize and lock to ground relay 815 through its No. 4 front contacts to grounded conductor 848 and relay 824 through its left No. 1 front contacts to grounded conductor 848. Relay 814, however,- which is pairedwith relay 815, remains short circuite'd since the operating ground on conductor 833 is so connected on the left side of the winding by way of the No. 1 back contacts of relay 814 Likewise, relay 813, which is paired with re lay 824, remains short circuiteddue to the ground on conductor 835 being likewise effestive on the left side of the Winding of relay 813 by way of its left innerback contacts,

As soon as relays 815 and 824 are operated,- ground from the bottom outer front contacts of relay 804, conductor 855,- N0. 4 contact's'of an relay824, left inner front contacts of relay 816 and winding of relay 806 shunts relay- 806,

thereby causing it to release, and the same ground on conductor 855 is also closed through the right Nos. 1 and 2 contacts of re lay 824 to conductor 869, left inner front contacts' of relay 817 and Winding of relay 811, shunting relay 811 and causing it to release also. Relays 816 and 81 7, however,- do not release because, with the release of relays 806 and 811, holding circuits for each of these relays are closed respectively, from battery through resistance 825, winding of relay 816, right inner normally made con tacts of relay 806, No. 4 contacts of relay 824, conductor 855 to ground on the bottom outer front contacts of relay "8 04, and battery, re-

' sistance 826, winding of relay 817, left inner normally made contacts of relay 811, right 7 Nos. 2 and 1 contactsof relay 824 to theaforetraced ground on conductor 855. 1

With the above described operated and normal condition of the relays shown in Figs. I 8 and 8A and during the period when relays 806 and 811 are releasing, the first impulse ist ransmitted. The order of the transmission: of impulses designating the wanted cuit at the distant ofiice and to light the lamp thereat to designate zero stations.

The transmission of impulses to the ca indicator oflice will now be described and the effect of these impulses at that oflicewill be considered hereinafter when describing the operation of the call indicator circuits.

Since no stations letter has been. dialed,

none of the relays in register 518 are operated and the first impulse of the four impulses representing the stations letter will, therefore, be a blank impulse, that is, the impulse time interval during which no current flow over the trunk loop to the call indicator of lice. This isapparent from an inspection of Figs. 8' and 8A. andithe operated or normal conditions of relays 815, 814, 824. and 813, 806 and 816, 811 and 817, 818 and 819 as previously described, The imipulse'time interval is measuredfr'om the time that ground is applied to the windingof relay 808- to thetime that the said relay is operated, as described hereinafter. With the above-mentioned relays that are operated in conjunction with those not operated, the trunk line conductor 447 isconnected to ground by way of the No.

3 bac'lrcontact of relay 803, t0p contacts of relay 823 to ground on the No. 2 contacts of re lay'803. Trunk conductor 448, however, is open at this time because it is connected through the combination of relays above operated to relay 523 of register 518 as follows: conductor 448, bottom inner back contacts of relay 803, bottominner contacts of relay 804,

conductor 844, right inner front contacts of relay 816,right inner front contacts of relay 817, right inner back contacts of relay 819,

conductor 870, left outer back contacts of re lay 821 which is normal, conductor 845, right back No. 2 contacts of relay 814, conductor 846 included in the bracket line 847, conductor 846, bracket line 847, conductor 846, Fig.

5, to the-leftcontact of relay 523. Since no stations letter was dialed, relay 523 is normal so that conductor 846 remains open at this relay, thereby resulting in a blank or open impulse on-the-trunk conductors connecting with the call indicator circuit at the terminating oflice.

During the time it takes to charge con denser 831 and relay 808 is normal, the first impulse is transmitted as'just described. When the condenser has become fully charged, the flow'of current through the 'up 

